Remove ehcache.xml file and ehcache dependency from oldcore

ehcache.xml is the configuration file for Ehcache.

Ehcache used to be the default second level cache of Hibernate but since Hibernate 3.2+ it's no longer the default (which is now no second level cache), and needs to be explicitely defined in hibernate.cfg.xml to be used (which we're not doing).

See:

• http://docs.jboss.org/hibernate/core/3.3/reference/en/html/performance.html#performance-cache
• http://stackoverflow.com/questions/5175346/which-implementation-is-hibernates-default-for-second-level-l2-cache

In addition we shouldn't have a second level cache set up since this would cause issues when our clustering is enabled.

We can thus safely remove ehache.xml since:

• the ehache.xml file is not used
• we don't need such a cache (since we do our own document level caching)
• it can cause issue in cluster mode